Low-frequency induction furnace

ABSTRACT

A low-frequency induction furnace in which molten metal reservoirs are provided on both sides of a primary coil, both reservoirs communicating with each other at their bottom portions by means of two secondary grooves extending across the primary coil. The bottom portion of each molten metal reservoir is of a size such that its cross-sectional area in the direction transverse to the direction of energization by induced current is smaller than that of each secondary groove. The induced current is induced in the molten metal in the reservoirs by energy from the primary coil.

United States Patent [1 1 Kohama 1 LOW-FREQUENCY INDUCTION FURNACE [75] Inventor: Masahiro Kohama, Yokohama,

Japan [73] Assignee: Kokusai Tekko Kabushiki Kaisha,

Yokohama-shi, Japan [22] Filed: Feb. 20, 1973 [21] App]. No.: 333,639

[52] U.S. Cl. 13/29, 13/28 [51] Int. Cl. H05b 5/12 [58] Field of Search 13/26, 28, 29

[56] References Cited UNITED STATES PATENTS 3,098,887 7/1963 Calamari 13/29 2,838,588 6/1958 Tagliaferri 13/28 1,786,322 12/1930 Unger 13/29 Jan. 15, 1974 Seede..- 13/28 Unger 13/28 Primary Examiner-Roy N. Envall, Jr. Att0rneyJames H. Littlepageet a1.

[57] ABSTRACT A low-frequency induction furnace in which molten metal reservoirs are provided on both sides of a primary coil, both reservoirs communicating with each other at their bottom portions by means of two secondary grooves extending across the primary coil. The bottom portion of each molten metal reservoir is of a size such that its cross-sectional area in the direction transverse to the direction of energization by induced current is smaller than that of each secondary groove. The induced current is induced in the molten metal in the reservoirs by energy fromthe primary coil.

4 Claims, 3 Drawing Figures 1. LOW-FREQUENCY INDUCTION FURNACE BACKGROUND OF THE INVENTION with two molten metal reservoirs have been used as a heat-supply source. Hence, in operation, the temperature in these grooves is elevated to the maximum occurring within the furnace, thereby causing excess wear and reduced durability of the furnace-body portions in the neighborhood of such secondary grooves. Further, since heat conductivity to the molten metalin the molten metal reservoirs is inadequate, heating efficiency is poor and excessive time is required for melting the metal. Still further, since the molten metal temperature in the secondary grooves reaches a local maximum, the viscosity of the molten metal in these parts becomes the lowest within the furnace, giving rise to a pinch effect in said grooves in the early phase of metal melting. Consequently, this pinch effect causes breakdown of the electric circuits and solidification of the molten metal, resulting in stoppage of the melting operation. Repairs of such damaged furnace bodies are extremely difficult and, in such case, a new furnace body usually must be built.

SUMMARY OF THE INVENTION The present invention relates to a device designed to eliminate such defects as found in the conventional furnaces of the type referred to, and to melt metal rapidly in the molten metal reservoirs by using as a heat source the heat generating grooves, which are provided in the bottom portionsof said reservoirs, and which are small BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a low-frequency induction furnace in accordance with the present invention;-

FIG. 2 is a sectional view taken along the line II-II of FIG. 1; and

FIG. 3 is a sectional view taken along the line III-III of FIG. I. I

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, a furnace body 1, composed of a water-proof electrically insulating material, has a central hole through which the central support 4 of an iron core 2 of a transformer extends. A primary coil 3 is wound around support 4. Molten metal reservoirs 7 and 8 are respectively situated on opposite sides of the primary coil 3 in the furnace body. In the bottom portions of reservoirs 7 and 8, heat-generating grooves 9 and 10 are respectively formed. Grooves 9 and 10 communicate with each other through secondary grooves 5 and 6 as'shown. Each of the heat generating grooves 9 and 10 is formed such that its sectional area in the direction or plane perpendicular to the direction of energization is smaller than that of each of secondary grooves 5 and 6. A molten metal outlet port 11 connects to reservoir 7.

In general, when molten metal is charged into the molten metal reservoirs 7 and 8 and secondary grooves 5 and 6 and then power is supplied to the primary coil 3, current flows through the shortest air passage constituted by the secondary grooves 5 and 6 and heat generating grooves 9 and 10. However, in the present invention, since the sectional area of each of the heat generating grooves 9 and 10 in the direction transverse to the direction of energization is smaller than that of each of said secondary grooves 5 and 6, the heat generating grooves 9 and 10 reach a local maximum temperature and allow the melting of metal in the reservoirs 7 and 8.

Thus, according to the present invention, since the heat generating grooves 9 and 10, which are provided at the bottom portions of the molten metal reservoirs 7 and 8 to serve as the heat source, are smaller in sectional area, therefore the current density developed in the heat generating grooves 9 and 10 becomes much greater. Hence, these parts become white-hot faster than the other parts and are more quickly lowered in viscosity. Consequently, the molten metal in the grooves 9 and 10 is expelled outwardly because of electromagnetic induction from the primary coil 3 which surrounds the central support 4 of the iron core. The molten metal in the reservoirs 7 and 8 flows into the heat generating grooves 9 and 10, and thus the heat is circulated naturally to effect quick and efficient melting of metal. Also, if any deterioration takes place in the furnace surrounding the heat generating section, such deteriorated portions can be repaired with ease. Further, should a pinch effect be created in the heat generating grooves 9 and 10 to cause solidification of molten metal with the molten metal flow being cutout, it-ispossible to complete an electric circuit immediately by adding new molten metal 'to the faulty part, thereby allowing continued operation without a stoppage.

What is claimed is:

'1. In a low-frequency induction furnace comprising:

A. a transformer primary coil, I

B. a pair of reservoirs for molten metal, the reservoirs being situated respectively on opposite sides of the primary coil, each reservoir including a grooved bottom portion,

C. two secondary grooves crossing the primary coil and located at the bottom portions of the reservoirs for interconnecting the pair of reservoirs, whereby current is induced in molten metal in the grooved bottom portion and in the two secondary grooves by induction from the primary coil, the improvement wherein the respective crosssectional areas in planes perpendicular to the direction of travel of the induced current of the grooved bottom portions and the two secondary grooves are such that said cross-sectional area of the grooved bottom portion is smaller than said cross-sectional area of the secondary grooves.

4 primary coil.

4. An induction furnace according to claim 2 wherein said heat-generating grooves are formed in the bottom portions of the respective molten metal reservoirs at a location closest to said primary coil. 

1. In a low-frequency induction furnace comprising: A. a transformer primary coil, B. a pair of reservoirs for molten metal, the reservoirs being situated respectively on opposite sides of the primary coil, each reservoir including a grooved bottom portion, C. two secondary grooves crossing the primary coil and located at the bottom portions of the reservoirs for interconnecting the pair of reservoirs, whereby current is induced in molten metal in the grooved bottom portion and in the two secondary grooves by induction from the primary coil, the improvement wherein the respective cross-sectional areas in planes perpendicular to the direction of travel of the induced current of the grooved bottom portions and the two secondary grooves are such that said cross-sectional area of the grooved bottom portion is smaller than said cross-sectional area of the secondary grooves.
 2. An induction furnace according to claim 1 wherein the grooved bottom portion comprises heat-generating grooves.
 3. An induction furnace according to claim 2 wherein said heat-generating grooves and said two secondary grooves are arranged to form a loop surrounding said primary coil.
 4. An induction furnace according to claim 2 wherein said heat-generating grooves are formed in the bottom portions of the respective molten metal reservoirs at a location closest to said primary coil. 